From 0f0e16becd40852863463c849633478787dc830a Mon Sep 17 00:00:00 2001
From: angelosa <lordkale4@gmail.com>
Date: Fri, 18 Oct 2024 00:40:49 +0200
Subject: [PATCH] video/upd7220.cpp: return 0xff on FIFO underflows * fix
 pc9821:skinpan intro hang

---
 hash/pc98.xml                 | 4 +++-
 src/devices/video/upd7220.cpp | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/hash/pc98.xml b/hash/pc98.xml
index 7434865fc2f..e94c5fb2f97 100644
--- a/hash/pc98.xml
+++ b/hash/pc98.xml
@@ -6767,8 +6767,10 @@ Never output any sound
 		<year>1993</year>
 		<publisher>ガイナックス (Gainax)</publisher>
 		<notes><![CDATA[
-Hangs during the intro (first dialogue)
+Hangs during the intro (first dialogue), [7220] FIFO underflows, worked around.
+Several [7220] invalid commands 0x05
 Draws Gainax logo with half height
+Title screen oddly keeps scrolling (verify)
 ]]></notes>
 		<info name="alt_title" value="バトルスキンパニック ９８２１" />
 		<info name="release" value="19930921" />
diff --git a/src/devices/video/upd7220.cpp b/src/devices/video/upd7220.cpp
index 8b8417e83f2..8bb8a9e8238 100644
--- a/src/devices/video/upd7220.cpp
+++ b/src/devices/video/upd7220.cpp
@@ -320,6 +320,12 @@ inline void upd7220_device::dequeue(uint8_t *data, int *flag)
 		if (m_fifo_ptr == -1)
 			m_sr &= ~UPD7220_SR_DATA_READY;
 	}
+	else
+	{
+		// TODO: underflow details
+		// pc9821:skinpan does SR checks over the wrong port during intro ...
+		*data = 0xff;
+	}
 }